An aromatic polyimide film shows a high heat resistance as well as good electric characteristics, and are widely employed as material for producing electronic devices. The aromatic polyimide film, however, has such a disadvantageous feature as poor adhesive property to an adhesive ordinarily employed for constituting electronic devices. Further, a metal film deposited on the aromatic polyimide film by sputtering shows poor adhesion to the polyimide film and is easily peeled off from the polyimide film. Therefore, studies for improving the poor adhesive property of an aromatic polyimide film have been made and reported.
U.S. Pat. No. 5,218,034 describes a polyimide film having improved adhesion and thermal durability containing from 0.02 to 1% by weight of tin based on the weight of the film.
U.S. Pat. No. 5,543,222 describes a vacuum metallized polyimide film comprising an aromatic polyimide layer containing a hydrocarbyl tin compound in oxidation states (II) or (IV) as an additive and metal plated layer bonded integrally with a high bonding strength or high adhesion through a vacuum deposited metal layer without the use of an adhesive.
U.S. Pat. No. 5,272,194 describes a strengthened polyimide film having improved adhesion when bonded to a metal foil through a heat-resistant adhesive, containing from 0.02 to 1% by weight, based on the weight of the film, of an organo-metallic compound wherein the metal is tin, bismuth or antimony.
U.S. Pat. No. 5,227,244 describes a polyimide film having improved adhesion prepared by coating the surface of a partially cured or partially dried polyamide acid film with an organic solvent solution of a metal salt and heating the coated film to both convert the polyamide acid to polyimide and dry the film. The metal salt is a salt of Sn, Zn, Cu, Fe, Co, Mn, or Pd.
Japanese Patent Provisional Publications 59-86634 and H2-134241 describe that a polyimide film can be improved in its adhesion by plasma discharge processing.
Japanese Patent Provisional Publication H1-214840 describes a process for preparing a polyimide pattern which comprises the steps of forming a film of an aluminum alcoholate or an aluminum chelate compound on a film of polyimide or its precursor, coating a photoresist on the aluminum-compound layer, imagewise exposing the photoresist coat to light, and etching the light-exposed photoresist.